The invention relates to an electric or hybrid electric vehicle comprising multiple drive units which drive units are arranged in separate parts of the vehicle. The multiple drive units are arranged to drive individual wheels or wheel axles in the vehicle.
The invention can be applied in heavy-duty vehicles, such as trucks, buses construction equipment and other work vehicles. Although the invention will be described with respect to an articulated bus, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as articulated or non-articulated trucks and construction equipment using multiple drive units located in different parts of the vehicle.
A problem with electric or hybrid electric road vehicles comprising multiple electric drive units and an increasing number of electrical components is related to pole-chassis capacitance. It is desirable to keep the pole-chassis capacitance below a predetermined value. In this context there are standards that set limits for the pole-chassis capacitance; for instance, ISO6469-3 requires energies lower than 0,2 Joule (J). As an example, in a vehicle comprising a high voltage electric system an energy of 0,2 J at 750 Volts (V) corresponds to a pole-chassis capacitance of 700*10−9 Farad (nF) at 750 V.
Each additional component in an electrical system adds additional capacitance to the system. A typical hybrid system can comprise a battery, an electric motor, a DC/DC converter, a compressor and an air-conditioning unit, which can contribute approximately 100 nF each. In addition, components such as a junction box and contactors contribute 10 nF each, along with cabling adding approximately 1 nF/m. This places a limitation to the maximum number of components that can be added to the electrical system.
A similar problem relates to the pole-chassis isolation resistance. For example, the electrical resistance between any part of the traction voltage system electrical circuit and another electrical system or any exposed part of the chassis may be selected to be greater than or equal to 100 Ω/V for DC components and 500 Ω/V for AC components. Also the total electrical resistance between any part of the traction voltage system electrical circuit and another electrical system or any exposed part of the chassis may be selected to be greater than or equal to 5000 kΩ. A system requirement of 500 Ω/V would give a total resistance of 375 kΩ at a system voltage of 750 V, which would allow for a maximum of 13 components.
It is desirable to provide an improved vehicle electrical system that eliminates or at least minimizes that above problems.
By the provision of electric or hybrid electric road vehicles comprising multiple electric drive units, or propulsion units, which are provided with an electrical architecture according to the invention, one advantage is that the number of electrical components can be increased without exceeding a predetermined value for the pole-chassis capacitance.
According to an aspect of the invention, the electric or hybrid electric vehicle has multiple drive units located in different parts of the vehicle, wherein a first driven axle is driven by at least one electric drive unit, and at least one further driven axle is driven by at least one electric drive unit. An electric drive unit comprises one or more electric motor, for driving the axle or each wheel on the axle, and an electric motor drive (EMD) for controlling the one or more electric motor. Each driven axle has at least one electric drive unit connected to a junction box and at least one energy storage system forming an electrical system. The junction box is connected to the electric motor drive, the energy storage system and other electrical components in the individual electrical system by high voltage DC buses.
According to one example, a vehicle according to the invention can have multiple electric drive units located in different parts of the vehicle. The vehicle comprises a front steerable axle and one or more additional axles, wherein two or more axles are driven. For example, an axle located in one part of the vehicle can have a first drive unit comprising at least an electric motor and a first energy storage system. At least one additional axle in a separate part of the vehicle can have a second drive unit comprising at least one further electric motor and an energy storage system. Hereby an improvement is that each drive unit comprises an individual electrical system which is galvanically isolated from the electrical systems of other drive unit at least under normal driving conditions.
According to a further example, a vehicle according to the invention can have at least two vehicle parts which are connected to and articulated relative to each other. The vehicle comprises a front vehicle part arranged at a front end of the vehicle, which front vehicle part has a front steerable axle and a rear driven axle, and at least one rear vehicle part having a single axle, which rear vehicle part is arranged behind the front vehicle part with respect to a longitudinal direction of the vehicle. The front vehicle part has a first drive unit comprising at least an electric motor and a first energy storage system. At least one rear vehicle part has a drive unit comprising at least an electric motor and an energy storage system. Hereby an improvement is that each rear vehicle part that comprises an individual electrical system is galvanically isolated from the front vehicle part and from each other at least under normal driving conditions.
Both the examples above can use one drive unit with an individual electrical system for each driven axle or for driving each wheel on a driven axle. Also, each driven axle can be driven by an electric drive unit, comprising one or more electric motors, or by a hybrid drive unit, comprising an electric motor and an internal combustion engine. An electronic control unit is provided for conjoint control of the drive unit for each axle.
In this context, the term “normal driving conditions” is defined as conditions where the vehicle is being driven using a traction system comprising an internal combustion engine and/or an electric motor, either in a traction mode drawing power from an associated power source or in regenerative mode supplying power to an energy storage unit within the vehicle.
According to an aspect of the invention, the individual electrical systems arranged in different parts of the vehicle are connectable during charging of at least one energy storage system from an external source of electrical power. The external source of electrical power can be provided from a charger via a conductive arrangement, such as plug-in socket or a pantograph, or an inductive arrangement, such as inductive coils in the road surface. Preferably, the individual electrical systems are connected to a common external charging unit. In the above examples, the energy storage systems in the individual electrical systems are primarily intended to be charged during periods when the vehicle is standing still. However, the use of, for instance, an overhead pantograph or induction coils in the road surface allows the vehicle to be charged while travelling.
The common external charging unit can be connected to the energy storage systems of an electrical system via at least one contactor, preferably using one contactor for each electrical system. The charging unit is arranged to control the voltage supplied to the energy storage unit or units being charged. The contactor is arranged to interrupt the flow of current through a circuit or to interrupt the supply of power to a circuit in order to isolate a part of a circuit from the supply. A suitable contactor for this purpose is a charging switch unit (CSU).
According to one example, individual electrical systems are connectable by a DC/DC converter, which in itself can provide galvanic isolation between the DC voltage buses in the respective electrical systems. The DC/DC converter can be connected between junction boxes in the respective electrical system. The DC/DC converter can be operable to adjust voltage to each DC voltage bus during charging of at least one energy storage system from an external source of power. For instance, if the voltage difference between the charger and the electrical system to be charged is too great, then it is not possible to close the contactor between the charger and the electrical system. In this case, the charge current can be passed through the DC/DC converter to supply a suitable voltage.
According to a further example, individual electrical systems are connectable by a DC bus comprising at least one contactor. Preferably, but not necessarily, a contactor is provided in the DC bus connecting each vehicle part comprising an energy storage system. This allows the DC bus in the individual electrical system in one vehicle part to be galvanically isolated from a DC bus connecting individual electrical systems in other parts of the vehicle. For instance, the common charger can be connected to the vehicle at one location, where after its DC bus is split into multiple DC buses, one for each individual electrical system. Each DC bus from the charger is connected to the junction box of each individual electrical system. A contactor is provided for each individual electrical system, so that the split DC bus can be disconnected when charging from an external source is not performed and the individual electrical systems are galvanically isolated.
As indicated above, each driven axle can be driven by an electric drive unit, comprising one or more electric motors. A vehicle driven by electric motors only is often referred to as a full electric vehicle (FEV). Alternatively, at least one axle can be driven by a hybrid drive unit, comprising an electric motor and an internal combustion engine. The internal combustion engine can be used for driving the axle, via a transmission, or for generating power for an electric motor or for an electric energy storage system. When the charger is of the plug-in type, such a vehicle is often referred to as a plug-in hybrid electric vehicle (PHEV).
A vehicle according to the invention comprises individual electrical systems each provided with an energy storage system. The energy storage system can comprise at least one battery, at least one super-capacitor and/or at least one source of mechanical and/or hydraulic energy. Within the scope of the invention, one energy storage system can be energy optimized, comprising battery cells, while a further system can be power optimized, comprising a super-capacitor, a source of mechanical and/or hydraulic energy.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.